NASA-Funded Research Discovers Life Built With Toxic Chemical

NASA-funded astrobiology research has changed the fundamental knowledge about what comprises all known life on Earth.

Researchers conducting tests in the harsh environment of Mono Lake in California have discovered the first known microorganism on Earth able to thrive and reproduce using the toxic chemical arsenic. The microorganism substitutes arsenic for phosphorus in its cell components.

"The definition of life has just expanded," said Ed Weiler, NASA's associate administrator for the Science Mission Directorate at the agency's Headquarters in Washington. "As we pursue our efforts to seek signs of life in the solar system, we have to think more broadly, more diversely and consider life as we do not know it."

This finding of an alternative biochemistry makeup will alter biology textbooks and expand the scope of the search for life beyond Earth. The research is published in this week's edition of Science Express.

Carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur are the six basic building blocks of all known forms of life on Earth. Phosphorus is part of the chemical backbone of DNA and RNA, the structures that carry genetic instructions for life, and is considered an essential element for all living cells.

Phosphorus is a central component of the energy-carrying molecule in all cells (adenosine triphosphate) and also the phospholipids that form all cell membranes. Arsenic, which is chemically similar to phosphorus, is poisonous for most life on Earth. Arsenic disrupts metabolic pathways because chemically it behaves similarly to phosphate.

"We know that some microbes can breathe arsenic, but what we've found is a microbe doing something new -- building parts of itself out of arsenic," said Felisa Wolfe-Simon, a NASA Astrobiology Research Fellow in residence at the U.S. Geological Survey in Menlo Park, Calif., and the research team's lead scientist. "If something here on Earth can do something so unexpected, what else can life do that we haven't seen yet?"

The newly discovered microbe, strain GFAJ-1, is a member of a common group of bacteria, the Gammaproteobacteria. In the laboratory, the researchers successfully grew microbes from the lake on a diet that was very lean on phosphorus, but included generous helpings of arsenic. When researchers removed the phosphorus and replaced it with arsenic the microbes continued to grow. Subsequent analyses indicated that the arsenic was being used to produce the building blocks of new GFAJ-1 cells.

The key issue the researchers investigated was when the microbe was grown on arsenic did the arsenic actually became incorporated into the organisms' vital biochemical machinery, such as DNA, proteins and the cell membranes. A variety of sophisticated laboratory techniques was used to determine where the arsenic was incorporated.

The team chose to explore Mono Lake because of its unusual chemistry, especially its high salinity, high alkalinity, and high levels of arsenic. This chemistry is in part a result of Mono Lake's isolation from its sources of fresh water for 50 years.

The results of this study will inform ongoing research in many areas, including the study of Earth's evolution, organic chemistry, biogeochemical cycles, disease mitigation and Earth system research. These findings also will open up new frontiers in microbiology and other areas of research.

"The idea of alternative biochemistries for life is common in science fiction," said Carl Pilcher, director of the NASA Astrobiology Institute at the agency's Ames Research Center in Moffett Field, Calif. "Until now a life form using arsenic as a building block was only theoretical, but now we know such life exists in Mono Lake."

The research team included scientists from the U.S. Geological Survey, Arizona State University in Tempe, Ariz., Lawrence Livermore National Laboratory in Livermore, Calif., Duquesne University in Pittsburgh, Penn., and the Stanford Synchroton Radiation Lightsource in Menlo Park, Calif.

NASA's Astrobiology Program in Washington contributed funding for the research through its Exobiology and Evolutionary Biology program and the NASA Astrobiology Institute. NASA's Astrobiology Program supports research into the origin, evolution, distribution, and future of life on Earth.

Man in the Moon has 'Graphite Whiskers'

PASADENA, Calif. -- In a new analysis of a lunar sample collected by Apollo 17, researchers have detected and dated carbon on the moon in the form of graphite -- the sooty stuff of pencil lead -- which survived from around 3.8 billion years ago, when the moon was heavily bombarded by meteorites. Up to now, scientists thought the trace amounts of carbon previously detected on the surface of the moon came from the solar wind.

Some of the graphite revealed by the new study appeared in a rare rolled form known as "graphite whiskers," which scientists believe formed in the very high-temperature reactions initiated by a meteorite impact. The discovery also means that the moon potentially holds a record of the carbon input by meteors into the Earth-moon system when life was just beginning to emerge on Earth. The research is published in the July 2 issue of the journal Science.

"The solar system was chaotic, with countless colliding objects 3.9 billion years ago," explained lead author Andrew Steele, based at the Carnegie Institution for Science in Washington, D.C. "Volatiles -- compounds like water and elements like carbon -- were vaporized under that heat and shock. These materials were critical to the creation of life on Earth."

"Materials that fell on the early Earth fell on the moon as well, because the two bodies basically share the same gravity well," said Marc Fries, a planetary scientist who conducted the research while working at NASA's Jet Propulsion Laboratory, Pasadena, Calif., and is now based at the Planetary Science Institute in Tucson, Ariz. "This sample is like a pristine page from Earth's past, before plate tectonics and other forces erased the history of this ancient carbon material on Earth."

While the sample from the Mare Serenitatis area came back to Earth in 1972, the research team, led by scientists at the Geophysical Laboratory of the Carnegie Institution for Science, used a new technique known as Raman spectroscopy on the sample. Previous techniques enabled scientists to get a sense of the composition, but this kind of spectroscopy is more sensitive and also allows scientists to create an image of the minerals. The graphite whiskers appeared to be a few micrometers in diameter and up to about 10 microns long.

Scientists were surprised at the finding of graphite and graphite whiskers.

"It shows that modern spatially resolved techniques could be used to discover further surprises in the now 40-year-old Apollo collection," said co-author Mihaela Glamoclija, based at the Carnegie Institution.

The scientists ruled out the possibility that the graphite was a result of contamination, because graphite whiskers, in particular, form under very hot conditions, between 1,830 and 6,500 degrees Fahrenheit (1,273 to 3,900 Kelvin). They also ruled out the solar wind as the source, because the graphite and graphite whiskers were much larger than carbon implanted by the solar wind, and while contamination occurred throughout the sample, the graphite was restricted to a discrete blackened area of the sample.

"We believe that the carbon we detected either came from the object that made the impact basin, or it condensed from the carbon-rich gas that was released during impact," said co-author Francis McCubbin, of the Carnegie Institution.

The research was partly funded by the NASA Astrobiology, Mars Fundamental Research, and the Lunar Advanced Science and Exploration Research programs in NASA's Planetary Division in Washington. The California Institute of Technology manages JPL for NASA.

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